Derived terms

Descendants

See also

Silver () is a chemical
element with the symbol "Ag" (lang-la argentum, from the Ancient
Greek: ἀργήντος - argēntos, gen. of ἀργήεις - argēeis, "white,
shining" ) and atomic number 47. A soft, white, lustrous transition
metal, it has the highest electrical conductivity of any
element and the highest thermal conductivity of any metal. It
occurs as a pure free metal (native silver) and alloyed with gold,
as well as in various minerals, such as argentite and chlorargyrite. Most silver
is produced as a by-product of copper, gold, lead, and zinc mining.

Occurrence and extraction

Silver is found in native form,
alloyed with gold or combined with sulfur, arsenic, antimony or chlorine in ores such as
argentite (Ag2S),
horn
silver (AgCl), and pyrargyrite (Ag3SbS3). The
principal sources of silver are the ores of copper, copper-nickel,
lead, and lead-zinc obtained from Peru, Mexico, China, Australia,
Chile and
Poland. Peru
and Mexico have been mining silver since 1546 and are still major
world producers. Top silver producing mines are Proano / Fresnillo,
Cannington, Dukat, Uchucchacua and Greens Creek mine..

The metal can also be produced during the
electrolytic
refining of copper and by the application of the Parkes
process on lead metal obtained from lead ores that contain
small amounts of silver. Commercial-grade fine silver is at least
99.9% pure silver, and purities greater than 99.999% are available.
In 2007, Peru
was the world's top producer of silver, closely followed by Mexico,
according to the British
Geological Survey.

Notable characteristics

Silver is a very ductile and
malleable
(slightly harder than gold)
monovalent coinage
metal with a brilliant white metallic luster that can take a
high degree of polish.
It has the highest electrical
conductivity of all metals, even higher than copper,
but its greater cost and tarnishability have prevented it
from being widely used in place of copper for electrical purposes,
though it was used in the electromagnets used for
enriching uranium during
World
War II (mainly because of the wartime shortage of copper).
Another notable exception is in high-end
audio cables, although the actual benefits of its use in this
application are questionable.

Isotopes

Naturally occurring silver is composed of the two
stable isotopes, 107Ag
and 109Ag, with 107Ag being the more abundant (51.839% natural
abundance). Silver's standard atomic mass is 107.8682(2) u.
Twenty-eight radioisotopes have been
characterised, the most stable being 105Ag with a half-life of
41.29 days, 111Ag with a half-life of 7.45 days, and 112Ag with a
half-life of 3.13 hours.

All of the remaining radioactive isotopes have
half-lives that are less than an hour, and the majority of these
have half-lives that are less than 3 minutes. This element has
numerous meta states,
the most stable being 108mAg (t* 418 years), 110mAg (t* 249.79
days) and 106mAg (t* 8.28 days).

The pallace isotope 107Pd decays by beta
emission to 107Ag with a half-life of 6.5 million years. Ironmeteorites are the only
objects with a high-enough palladium-to-silver ratio to yield
measurable variations in 107Ag abundance. Radiogenic 107Ag
was first discovered in the Santa
Clara meteorite in 1978. The discoverers suggest that the
coalescence and differentiation of iron-cored small planets may have occurred 10
million years after a nucleosynthetic event.
107Pd–107Ag correlations observed in bodies that have clearly been
melted since the accretion
of the solar system
must reflect the presence of live short-lived nuclides in the early
solar system.

Applications

As a precious metal

A major use of silver is as a precious
metal and it has long been used for making high-value objects
reflecting the wealth and status of the owner. Jewellery and
silverware are traditionally made from sterling
silver (standard silver), an alloy of 92.5% silver with 7.5%
copper. Sterling silver is harder than pure silver and has a lower
melting point (893 °C) than either pure silver or pure copper.
Britannia
silver is an alternative hallmark-quality standard containing
95.8% silver, often used to make silver tableware and wrought
plate. With the addition of germanium, the patented
modified alloy Argentium
Sterling Silver is formed, with improved properties including
resistance to firescale.

Silver is used in medals, denoting second place.
Some high-end musical
instruments are made from sterling silver, such as the flute.

In dentistry

Silver dissolves in mercury to make amalgams that are widely used
for dental fillings. To make dental amalgam, a mixture of powdered
silver and other metals is mixed with mercury to make a stiff paste
that can be moulded into shape in a cavity, but which sets hard
within a few hours.

In photography and electronics

Photography used 24% of the
silver consumed in 2001 in the form of silver
nitrate and silver halides, while 33% was used in
jewellery, 40% for industrial uses, and only 3% for coins and
medals.

Some electrical and electronic products use
silver for its superior conductivity, even when tarnished. For
example, printed
circuits are made using silver paints, and computer keyboards
use silver electrical contacts. Some high-end audio hardware
(DACs,
preamplifiers,
etc.) are fully silver-wired, which is believed to cause the least
loss of quality in the signal. Silver cadmium oxide is used in high
voltage contacts because it can withstand arcing.

In mirrors and optics

Mirrors which need
superior reflectivity for visible light are made with silver as the
reflecting material in a process called silvering, though common
mirrors are backed with aluminium. Using a process called sputtering, silver (and
sometimes gold) can be applied to glass at various thicknesses,
allowing different amounts of light to penetrate. Silver is usually
reserved for coatings of specialised optics, and the silvering most
often seen in architectural glass and tinted windows on vehicles is
produced by sputtered aluminium, which is cheaper and less
susceptible to tarnishing and corrosion.

As a catalyst

Silver's catalytic properties make it ideal
for use as a catalyst
in oxidation reactions, for example, the production of formaldehyde from methanol and air by means of
silver screens or crystallites containing a
minimum 99.95 weight-percent silver. Silver (upon some
suitable support) is probably the only catalyst available today to
convert ethylene to
ethylene
oxide (later hydrolyzed to ethylene
glycol, used for making polyesters)—a very important
industrial reaction.

Oxygen dissolves in
silver relatively easily compared to other gases present in air.
Attempts have been made to construct silver membranes
of only a few monolayers thickness. Such a
membrane could be used to filter pure oxygen from air.

As money

Silver, in the form of electrum, was coined to produce
money in around 700 BCE by the Lydians. Later,
silver was refined and coined in its pure form (see silver coin).
Many nations used silver as the basic unit of monetary value (see
Silver
standard). The words for "silver" and "money" are the same in
at least 14 languages. In the modern world, silver bullion has the ISO currency
code XAG.

The name of the United Kingdom monetary unit
"pound" reflects the fact that it originally represented the value
of one troy pound of
sterling silver.

In medicine

Silver ions and silver compounds show a toxic
effect on some bacteria, viruses, algae and fungi, typical for
heavy metals like lead or
mercury,
but without the high toxicity to humans that is normally associated
with them. Its germicidal effects kill many microbial organisms
in
vitro.

Hippocrates,
the father of modern medicine, wrote that silver had beneficial
healing and anti-disease properties, and the Phoenicians
used to store water, wine,
and vinegar in silver
bottles to prevent spoiling. In the early 1900s people would put
silver
dollars in milk bottles to prolong the milk's freshness. Its
germicidal effects increase its value in utensils and as jewellery.
The exact process of silver's germicidal effect is still not well
understood, although theories exist. One of these is the oligodynamic
effect, which explains the effect on microbial lifeforms but
does not explain certain antiviral effects.

Silver compounds were used successfully to
prevent infection in World War I
before the advent of antibiotics. Silver nitrate
solution was a standard of care but was largely replaced by
silver
sulfadiazine cream (SSD Cream) which was generally the
"standard of care" for the antibacterial and antibiotic treatment
of serious burns until the late 1990s. Now, other options, such as
silver-coated dressings (activated silver dressings), are used in
addition to SSD cream and may present advantages such as pain
reduction and capacity for treatment at home.

The widespread use of silver went out of fashion
with the development of modern antibiotics. However, recently there
has been renewed interest in silver as a broad-spectrum
antimicrobial. In particular, silver is being used with alginate, a naturally occurring
biopolymer derived
from seaweed, in a range of products designed to prevent infections
as part of wound
management procedures, particularly applicable to burn
victims. In 2007, AGC Flat
Glass Europe introduced the first antibacterial glass to fight
hospital-caught infection: it is covered with a thin layer of
silver. In addition, Samsung has
introduced washing
machines with a final rinse containing silver ions to provide
several days of antibacterial protection in the clothes. Kohler has
introduced a line of toilet seats
that have silver ions embedded to kill germs. A company called
Thomson Research Associates has begun treating products with Ultra
Fresh, an anti-microbial technology involving "proprietary
nano-technology to produce the ultra-fine silver particles
essential to ease of application and long-term protection." The
FDA has
recently approved an endotracheal
breathing tube with a fine coat of silver for use in mechanical
ventilation, after studies found it reduced the risk of
ventilator-associated pneumonia.

As a medication

Today, various kinds of silver compounds,
or devices to make solutions or colloids containing silver, are
sold as remedies for a wide variety of diseases. Although most
colloidal
silver preparations are harmless, some people using these
home-made solutions excessively have developed argyria over a period of months
or years. Several cases have been documented in medical literature,
including one case of coma associated with high intake of silver.
It is strongly advised to consult a doctor before embarking on such
treatment.

Silver is widely used in topical gels and
impregnated into bandages because of its wide-spectrum
antimicrobial activity. The anti-microbial properties of silver
stem from the chemical properties of its ionized form, Ag+. This
ion forms strong molecular bonds with other substances used by
bacteria to respire,
such as molecules containing sulfur, nitrogen, and oxygen. Once the Ag+ ion
complexes with these molecules, they are rendered unusable by the
bacteria, depriving it of necessary compounds and eventually
leading to the bacteria's death.

In food

In India, foods,
especially sweets, can be found decorated with a thin layer of
silver known as vark.
Silver as a food additive is given the E numberE174 and is
classed as a food
coloring. It is used solely for external decoration, such as on
chocolate
confectionery, in the covering of dragées and
the decoration of sugar-coated flour confectionery. In Australia, it is
banned as a food additive.

In clothing

Silver inhibits the growth of bacteria and fungi. It keeps odour to a minimum and reduces the
risk of bacterial and fungal infection. In clothing, the
combination of silver and moisture movement (wicking) may help to
reduce the harmful effects of prolonged use in active and humid
conditions.

In both cases the silver prevents the growth of a broad
spectrum of bacteria and fungi.

Recorded use of silver to prevent infection dates
to ancient
Greece and Rome. It was
rediscovered in the Middle Ages,
where it was used for several purposes, such as to disinfect water
and food during storage, and also for the treatment of burns and
wounds as wound dressing. In the 19th century, sailors on long
ocean voyages would put silver coins in barrels of water and
wine to keep the liquid
pure. Pioneers in America used the same idea as they made their
journey from coast to coast. Silver solutions were approved in the
1920s by the
US Food and Drug Administration for use as antibacterial
agents. Today, wound dressings containing silver are well
established for clinical wound care and have recently been
introduced in consumer products such as sticking plasters.

History

The word "silver" appears in Anglo-Saxon
in various spellings such as seolfor and siolfor. A similar form is
seen throughout the Teutonic languages (compare Old High
German silabar and silbir). The symbol "Ag" is from the Latin
for "silver", argentum (compare Greek αργυρος (argyros)), from the
Indo-European root arg- meaning "white" or "shining".

Price

Silver is currently about 1/50th the price of
gold by mass and
approximately 70 times more valuable than copper. Silver once traded at
1/6th to 1/12th the price of gold, prior to the Age of
Discovery and the discovery of great silver deposits in the
Americas, most notably the vast Comstock
Lode in Virginia
City, Nevada, USA. This
then resulted in the debate over cheap Free Silver
to benefit the agricultural sector, which was among the most
prolonged and difficult in that country's history and dominated
public discourse during the latter decades of the nineteenth
century.

Over the last 100 years the price of silver and
the gold/silver price ratio have fluctuated greatly due to
competing industrial and store-of-value
demands. In 1980 the silver price rose to an all-time high of
US$49.45 per troy ounce. By
December 2001 the price had dropped to US$4.15 per ounce, and in
May 2006 it had risen back as high as US$15.21 per ounce. As of
2006, silver prices (and most other metal prices) have been rather
volatile, for example, quickly dropping from the May high of
US$15.21 per ounce to a June low of US$9.60 per ounce before rising
back above US$12.00 per ounce by August. In March 2008 silver
reached US$21.34 per ounce.

The price of silver is important in Judaic Law.
The lowest fiscal amount
that a Jewish court, or Beth Din, can
convene to adjudicate a case over is a shova pruta (value of a
Babylonian prutra coin). This is fixed at 1/8 of a gram of pure,
unrefined silver, at market price.

Folklore and popular culture

Silver in European
folklore has long been traditionally believed to be an antidote
to various maladies and mythical monsters. Notably, silver was
believed to be a repellent against vampires (this primarily
originates from its holy connotations; also, mirrors were
originally polished silver, and as such, vampires allegedly cannot
be seen in them because they have no soul) and it was also believed
that a werewolf, in his
bestial form, could only be killed by a weapon or bullet made of
silver. This has given rise to the term "silver
bullet", which is used to describe things that very effectively
deal with one specific problem.

In heraldry, the tincture
argent, in addition to being shown as silver (this has been
shown at times with real silver in official representations), can
also be shown as white. Occasionally, the word "silver" is used
rather than argent; sometimes this is done across-the-board,
sometimes to avoid repetition of the word "argent" in blazon.

Precautions

Silver plays no known natural biological role
in humans, and possible health effects of silver are a subject of
dispute. Silver itself is not toxic but most silver
salts are, and some may be carcinogenic.

Silver and compounds containing silver (like
colloidal
silver) can be absorbed into the circulatory
system and become deposited in various body tissues leading to
a condition called argyria which results in a
blue-grayish pigmentation of the skin, eyes, and mucous
membranes. Although this condition does not harm a person's
health, it is disfiguring and usually permanent. Argyria is rare,
and mild forms are sometimes mistaken for cyanosis.